High strength aluminum alloys for low pressure die casting and gravity casting

ABSTRACT

Methods of casting lightweight, high-strength aluminum cast structural components are provided wherein the casting is accomplished by low-pressure die casting or gravity casting. The aluminum cast structural component is preferably composed of an aluminum-based alloy comprising silicon at ≥about 4 to ≥about 7 wt. %; iron at ≥about 0.15 wt. %; manganese at ≥about 0.5 wt. %; chromium at ≥about 0.15 to ≥about 0.5 wt. %; magnesium at ≥about 0.8 wt. %; zinc at ≥about 0.01 wt. %; titanium at ≥about 0.05 to ≥about 0.15 wt. %; phosphorus at ≥about 0.003 wt. %; strontium at ≥about 0.015 wt. % and a balance of aluminum.

FIELD

The present disclosure relates to methods of casting metal componentsand more particularly to methods of casting metal components fromaluminum-based metal alloy compositions.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Aluminum-based alloys are generally classified into two distinctcategories: cast and wrought alloys. Both types of alloys are inwidespread use throughout many industries, including in the automotiveindustry. Wrought alloys typically offer greater yield strengths thancast alloys. Cast alloys, however, are generally cheaper to produce thanwrought alloys; further, cast alloys offer yield strengths sufficientfor many applications. For example, one suitable wrought aluminum alloy,A6061, offers a yield strength of greater than or equal to about 270 toless or equal to than about 310 MPa, whereas a suitable cast aluminumalloy, A356, offers a yield strength of greater than or equal to about150 to less than or equal to about 180 MPa.

Turning to cast alloys specifically, aluminum-based alloy cast parts canbe produced by conventional casting methods which include die-casting,sand casting, permanent and semi-permanent mold casting, plaster-moldcasting and investment casting. Cast parts are generally formed bypouring a molten metal into a casting mold or die that provides shape tothe molten material as it cools and solidifies. The mold or die is laterseparated from the part after solidification.

While many cast alloys offer yield strengths sufficient for manyapplications, there is a continual need to prepare cast moldings havingincreased yield strengths. There is a further need to reduce the mass ofvehicle components for improved fuel efficiency without sacrificingrequisite yield strengths.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In various aspects, the present disclosure provides a method of forminga lightweight, high-strength cast structural component comprisingcasting an aluminum-based alloy. The aluminum-based alloy has acomposition comprising silicon at greater than or equal to about 4 toless than or equal to about 7 wt. %; iron at less than or equal to about0.15 wt. %; manganese at less than about 0.5 wt. %; chromium at greaterthan or equal to about 0.15 to less than or equal to about 0.5 wt. %;magnesium at less than or equal to about 0.8 wt. %; zinc at less than orequal to about 0.01 wt. %; titanium at greater than or equal to about0.05 to less than or equal to about 0.15 wt. %; phosphorus at less thanor equal to about 0.003 wt. %; strontium at less than or equal to about0.015 wt. %; and a balance of aluminum. The lightweight, high-strengthcast structural component may have a yield strength of greater than orequal to about 270 to less than or equal to about 300 MPa. Thelightweight, high-strength cast structural component may have anelongation of greater than or equal to about 7%, and, more preferably,greater than or equal to about 9%. The casting may be produced bylow-pressure die casting or gravity casting processes. The lightweight,high-strength cast structural component may be heat treated aftercasting. In certain aspects, the heat treatment can be a T6 heattreatment, where the cast structural component is immersed in a solutionfollowed by quenching, followed by artificial aging. When low-pressuredie casting is contemplated, the presence of magnesium may be furtherlimited to from greater than or equal to about 0.1 to less than or equalto about 0.6 wt. % and the presence of strontium may be further limitedto from greater than or equal to about 0.001 to less than or equal toabout 0.015 wt. %. When gravity casting is contemplated, the presence ofmagnesium may be further limited to from greater than or equal to about0.1 to less than or equal to about 0.5 wt. %; the phosphorus may befurther limited to an amount of less than or equal to about 0.001 wt. %;and the presence of strontium may be further limited to an amount ofless than or equal to about 0.005 wt. %.

In yet other aspects, the present disclosure provides a method offorming a lightweight, high-strength cast structural componentcomprising casting an aluminum-based alloy by gravity casting. Thealuminum-based alloy has a composition comprising silicon at greaterthan or equal to about 4 to less than or equal to about 7 wt. %; iron atless than or equal to about 0.15 wt. %; manganese at less than or equalto about 0.5 wt. %; chromium at greater than or equal to about 0.15 toless than or equal to about 0.5 wt. %; magnesium at less than or equalto about 0.8 wt. %; zinc at less than or equal to about 0.01 wt. %;titanium at greater than or equal to about 0.05 to less than or equal toabout 0.15 wt. %; strontium at less than or equal to about 0.015 wt. %;phosphorus at less than or equal to about 0.003 wt. %; and a balance ofaluminum. The lightweight, high-strength cast structural componentfurther may have a yield strength of greater than or equal to about 270to less than or equal to about 300 MPa. The casting may be low-pressuredie casting or gravity casting. The lightweight, high-strength caststructural component may be heat treated after casting. In certainaspects, the heat treatment can be a T6 heat treatment, where the caststructural component is immersed in a solution followed by quenching,followed by artificial aging. The cast structural component may have anelongation of greater than or equal to about 7%. The presence ofmagnesium may be further limited to from greater than or equal to about0.1 to less than or equal to about 0.5 wt. %; the phosphorus may befurther limited to an amount of less than or equal to about 0.001 wt. %;and the presence of strontium may be further limited to an amount ofless than or equal to about 0.005 wt. %.

In yet other aspects, the present disclosure provides a method offorming a lightweight, high-strength cast structural componentcomprising an aluminum-based alloy is formed from a casting bylow-pressure die casting. The alloy material has a compositioncomprising silicon at greater than or equal to about 4 to less than orequal to about 7 wt. %; iron at less than or equal to about 0.15 wt. %;manganese at less than or equal to about 0.5 wt. %; chromium at greaterthan or equal to about 0.15 to less than or equal to about 0.5 wt. %;magnesium at less than or equal to about 0.8 wt. %; zinc at less than orequal to about 0.01 wt. %; titanium at greater than or equal to about0.05 to less than or equal to about 0.15 wt. %; phosphorus at less thanor equal to about 0.003 wt. %; strontium at less than or equal to about0.015 wt. %; and a balance of aluminum. The lightweight, high-strengthcast structural component further may have a yield strength of greaterthan or equal to about 270 to less than or equal to about 300 MPa. Thelightweight, high-strength cast structural component may have anelongation of greater than or equal to about 7%, and, more preferably,greater than or equal to about 9%. The lightweight, high-strength caststructural component may be heat treated after casting. In certainvariations, the heat treatment can be a T6 heat treatment where the caststructural component is immersed in a solution followed by quenching,followed by artificial aging. The presence of magnesium may be furtherlimited to greater than or equal to about 0.1 to less than or equal toabout 0.6 wt. % and the presence of strontium may be further limited togreater than or equal to about 0.001 to less than or equal to about0.015 wt. %.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 shows a representative wheel manufactured according to an aspectof this invention.

FIG. 2 shows a flowchart of an exemplary process for preparing alightweight, high-strength cast structural component according to anembodiment of the present disclosure.

FIG. 3 shows a flowchart of an exemplary process for preparing alightweight, high-strength cast structural component according to analternative embodiment of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

The following description of the various aspects of the presentdisclosure is merely exemplary in nature and is in no way intended tolimit the invention, its application, or uses.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific compositions, components, devices, and methods, to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to those skilled in the art that specific details need notbe employed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed, unless otherwiseindicated.

Although the terms first, second, third, etc. may be used herein todescribe various steps, elements, components, regions, layers and/orsections, these steps, elements, components, regions, layers and/orsections should not be limited by these terms, unless otherwiseindicated. These terms may be only used to distinguish one step,element, component, region, layer or section from another step, element,component, region, layer or section. Terms such as “first,” “second,”and other numerical terms when used herein do not imply a sequence ororder unless clearly indicated by the context. Thus, a first step,element, component, region, layer or section discussed below could betermed a second step, element, component, region, layer or sectionwithout departing from the teachings of the example embodiments.

Spatially or temporally relative terms, such as “before,” “after,”“inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and thelike, may be used herein for ease of description to describe one elementor feature's relationship to another element(s) or feature(s) asillustrated in the figures. Spatially or temporally relative terms maybe intended to encompass different orientations of the device or systemin use or operation in addition to the orientation depicted in thefigures.

It should be understood for any recitation of a method, composition,device, or system that “comprises” certain steps, ingredients, orfeatures, that in certain alternative variations, it is alsocontemplated that such a method, composition, device, or system may also“consist essentially of” the enumerated steps, ingredients, or features,so that any other steps, ingredients, or features that would materiallyalter the basic and novel characteristics of the invention are excludedtherefrom.

Throughout this disclosure, the numerical values represent approximatemeasures or limits to ranges to encompass minor deviations from thegiven values and embodiments having about the value mentioned as well asthose having exactly the value mentioned. Other than in the workingexamples provided at the end of the detailed description, all numericalvalues of parameters (e.g., of quantities or conditions) in thisspecification, including the appended claims, are to be understood asbeing modified in all instances by the term “about” whether or not“about” actually appears before the numerical value. “About” indicatesthat the stated numerical value allows some slight imprecision (withsome approach to exactness in the value; approximately or reasonablyclose to the value; nearly). If the imprecision provided by “about” isnot otherwise understood in the art with this ordinary meaning, then“about” as used herein indicates at least variations that may arise fromordinary methods of measuring and using such parameters. If, for somereason, the imprecision provided by “about” is not otherwise understoodin the art with this ordinary meaning, then “about” as used herein mayindicate a possible variation of up to 5% of the indicated value or 5%variance from usual methods of measurement.

In addition, disclosure of ranges includes disclosure of all values andfurther divided ranges within the entire range, including endpoints andsub-ranges given for the ranges.

In various aspects, the present disclosure provides methods of casting astrong, lightweight aluminum-based alloy. By “aluminum-based” it ismeant that the composition is primarily comprised of aluminum, generallygreater than or equal to about 90 wt. % aluminum. As used herein, theterm “composition” refers broadly to a substance containing at least thepreferred metal elements or compounds, but which may also compriseadditional substances or compounds, including additives and impurities.The term “material” also broadly refers to matter containing thepreferred compounds or composition. The present disclosure furtherrelates to methods of making preferred embodiments of the aluminum-basedalloy, as well as to methods of making components with preferredembodiments of the inventive alloy.

“Low-pressure die casting” as used herein is a type of metal castingprocess where typically a metal melt is in a sealed furnace having ariser tube at a pressure of less than or equal to about 0.7 bar (atleast in certain variations). A die may be connected to the riser tubeand positioned above the sealed furnace having the metal melt.Optionally, a degasser is introduced to reduce gasses present in themetal melt. A pressurized gas is introduced into the sealed furnace,which forces the metal melt through the riser tube and into the die. Thepressurized gas is kept for a duration sufficient to fill the die withthe metal melt and to allow the metal melt in the die to solidify. Oncethe casting solidifies, the pressurized gas is released, the metal meltin the riser tube returns to the sealed furnace, and the die opens torelease the casting. The process may then be repeated after closing thedie.

“Gravity casting” as used herein is a type of metal casting processwhere a metal melt is introduced into a die by a pouring cup or a ladleor the like. Optionally, a degasser is introduced to reduce gassespresent in the metal melt. After solidification, the die is opened andthe casting removed.

“T6 heat treatment” as used herein is a two-step heat treatment processinvolving a solution treatment with hot-water quenching, followed by anartifical aging treatment. By way of example, the first step generallyinvolves providing a solution treatment by heating a casting to fromgreater than or equal to about 535° C. to less than or equal to about545° C. for a period of less than or equal to about eight hours,followed by hot water quenching at from greater than or equal to about70° C. to less than or equal to about 90° C. The second step generallyinvolves an artificial aging treatment, wherein the casting is subjectto a temperature of from greater than or equal to about 4 to less thanor equal to about 20 hours.

The present disclosure provides methods of forming a lightweight,high-strength cast structural component. High-strength, lightweightalloy components are particularly suitable for use in components of anautomobile or other vehicle (e.g., motorcycles, boats), but may also beused in a variety of other industries and applications, includingaerospace components, industrial equipment and machinery, farmequipment, heavy machinery, by way of non-limiting example. While notlimiting, the present methods and materials are particularly suitablefor forming lightweight, high-strength components for a vehicle,including chassis and powertrain castings, such as wheels, lightweightvalves, lightweight pistons, knuckles, control arms, and engine blocks,and additional powertrain components such as oil pans and engine heads,by way of non-limiting example.

Referring first to FIG. 1, an exemplary automotive structural component,such as wheel 10, is shown that can be produced from the casting methodsdisclosed herein. In certain variations, a lightweight, high-strengthcast structural component according to the present disclosure may becast by low-pressure die casting or gravity casting. After casting, thelightweight, high-strength cast structural component is furthersubjected to a heat treatment process and more preferably to a T6 heattreatment process. The lightweight, high-strength cast structuralcomponent may be formed of an aluminum-based alloy material having acomposition comprising silicon at greater than or equal to about 4 toless than or equal to about 7 wt. %; iron at less than or equal to about0.15 wt. %; manganese at less than or equal to about 0.5 wt. %; chromiumat greater than or equal to about 0.15 to less than or equal to about0.5 wt. %; magnesium at less than or equal to about 0.8 wt. %; zinc atless than or equal to about 0.01 wt. %; titanium at greater than orequal to about 0.05 to less than or equal to about 0.15 wt. %;phosphorus at less than or equal to about 0.003 wt. %; strontium at lessthan or equal to about 0.015 wt. %; and a balance of aluminum. Incertain embodiments, the magnesium is present in an amount of greaterthan or equal to about 0.1 to less than or equal to about 0.6 wt. % andthe strontium is present in an amount of greater than or equal to about0.01 to less than or equal to about 0.015 wt. %. In yet otherembodiments, the magnesium is present in an amount of from greater thanor equal to about 0.1 to less than or equal to about 0.5 wt. %; thephosphorus is present in an amount of less than or equal to about 0.001wt. %; and the strontium is present in an amount of less than or equalto about 0.005 wt. %.

In yet other embodiments, the lightweight, high-strength cast structuralcomponent is formed of an aluminum-based alloy material having acomposition consisting essentially of silicon at greater than or equalto about 4 to less than or equal to about 7 wt. %; iron at less than orequal to about 0.15 wt. %; manganese at less than or equal to about 0.5wt. %; chromium at greater than or equal to about 0.15 to less than orequal to about 0.5 wt. %; magnesium at less than or equal to about 0.8wt. %; zinc at less than or equal to about 0.01 wt. %; titanium atgreater than or equal to about 0.05 to less than or equal to about 0.15wt. %; phosphorus at less than or equal to about 0.003 wt. %; strontiumat less than or equal to about 0.015 wt. %; and a balance of aluminum.In still other embodiments, the lightweight, high-strength caststructural component is preferably formed of an aluminum-based alloymaterial having a composition consisting of silicon at greater than orequal to about 4 to less than or equal to about 7 wt. %; iron at lessthan or equal to about 0.15 wt. %; manganese at less than or equal toabout 0.5 wt. %; chromium at greater than or equal to about 0.15 to lessthan or equal to about 0.5 wt. %; magnesium at less than or equal toabout 0.8 wt. %; zinc at less than or equal to about 0.01 wt. %;titanium at greater than or equal to about 0.05 to less than or equal toabout 0.15 wt. %; phosphorus at less than or equal to about 0.003 wt. %;strontium at less than or equal to about 0.015 wt. %; and a balance ofaluminum. In yet other embodiments, the lightweight, high-strength caststructural component is preferably formed of an aluminum-based alloymaterial having a composition consisting essentially of silicon atgreater than or equal to about 4 to less than or equal to about 7 wt. %;iron at less than or equal to about 0.15 wt. %; manganese at less thanor equal to about 0.5 wt. %; chromium at greater than or equal to about0.15 to less than or equal to about 0.5 wt. %; magnesium at greater thanor equal to about 0.1 to less than or equal to about 0.6 wt. %; zinc atless than or equal to about 0.01 wt. %; titanium at greater than orequal to about 0.05 to less than or equal to about 0.15 wt. %;phosphorus at less than or equal to about 0.003 wt. %; strontium atgreater than or equal to about 0.01 to less than or equal to about 0.015wt. %; and a balance of aluminum. In still other embodiments, thelightweight, high-strength cast structural component is preferablyformed of an aluminum-based alloy material having a compositionconsisting of silicon at greater than or equal to about 4 to less thanor equal to about 7 wt. %; iron at less than or equal to about 0.15 wt.%; manganese at less than or equal to about 0.5 wt. %; chromium atgreater than or equal to about 0.15 to less than or equal to about 0.5wt. %; magnesium at greater than or equal to about 0.1 to less than orequal to about 0.6 wt. %; zinc at less than or equal to about 0.01 wt.%; titanium at greater than or equal to about 0.05 to less than or equalto about 0.15 wt. %; phosphorus at less than or equal to about 0.003 wt.%; strontium at greater than or equal to about 0.01 to less than orequal to about 0.015 wt. %; and a balance of aluminum.

In yet other embodiments, the lightweight, high-strength cast structuralcomponent is formed of an aluminum-based alloy material having acomposition consisting essentially of silicon at greater than or equalto about 4 to less than or equal to about 7 wt. %; iron at less than orequal to about 0.15 wt. %; manganese at less than or equal to about 0.5wt. %; chromium at greater than or equal to about 0.15 to less than orequal to about 0.5 wt. %; magnesium at greater than or equal to about0.1 to less than or equal to about 0.5 wt. %; zinc at less than or equalto about 0.01 wt. %; titanium at greater than or equal to about 0.05 toless than or equal to about 0.15 wt. %; phosphorus at less than or equalto about 0.001 wt. %; strontium at less than or equal to about 0.005 wt.%; and a balance of aluminum. In still other embodiments, thelightweight, high-strength cast structural component is formed of analuminum-based alloy material having a composition consisting of siliconat greater than or equal to about 4 to less than or equal to about 7 wt.%; iron at less than or equal to about 0.15 wt. %; manganese at lessthan or equal to about 0.5 wt. %; chromium at greater than or equal toabout 0.15 to less than or equal to about 0.5 wt. %; magnesium atgreater than or equal to about 0.1 to less than or equal to about 0.5wt. %; zinc at less than or equal to about 0.01 wt. %; titanium atgreater than or equal to about 0.05 to less than or equal to about 0.15wt. %; phosphorus at less than or equal to about 0.001 wt. %; strontiumat less than or equal to about 0.005 wt. %; and a balance of aluminum.

In yet other embodiments, the lightweight, high-strength cast structuralcomponent may be formed of an aluminum-based alloy material having acomposition comprising silicon at greater than or equal to about 4.5 toless than or equal to about 5.5 wt. %; iron at less than or equal toabout 0.15 wt. %; chromium at greater than or equal to about 0.25 toless than or equal to about 0.35 wt. %; magnesium at less than or equalto about 0.5 wt. %; zinc at less than or equal to about 0.01 wt. %;titanium at greater than or equal to about 0.05 to less than or equal toabout 0.1 wt. %; phosphorus at less than or equal to about 0.003 wt. %;strontium at less than or equal to about 0.015 wt. %; and a balance ofaluminum. In certain embodiments, the magnesium is present in an amountof greater than or equal to about 0.1 to less than or equal to about 0.5wt. % and the strontium is present in an amount of greater than or equalto about 0.01 to less than or equal to about 0.015 wt. %. In yet otherembodiments, the magnesium is present in an amount of from greater thanor equal to about 0.1 to less than or equal to about 0.3 wt. %; thephosphorus is present in an amount of less than or equal to about 0.001wt. %; and the strontium is present in an amount of less than or equalto about 0.005 wt. %. In yet other embodiments, the lightweight,high-strength cast structural component is formed of an aluminum-basedalloy material having a composition consisting essentially of silicon atgreater than or equal to about 4.5 to less than or equal to about 5.5wt. %; iron at less than or equal to about 0.15 wt. %; chromium atgreater than or equal to about 0.25 to less than or equal to about 0.35wt. %; magnesium at greater than or equal to about 0.1 to less than orequal to about 0.5 wt. %; zinc at less than or equal to about 0.01 wt.%; titanium at greater than or equal to about 0.05 to less than or equalto about 0.1 wt. %; phosphorus at less than or equal to about 0.003 wt.%; strontium at greater than or equal to about 0.01 to less than orequal to about 0.015 wt. %; and a balance of aluminum. In still otherembodiments, the lightweight, high-strength cast structural component isformed of an aluminum-based alloy material having a compositionconsisting of silicon at greater than or equal to about 4.5 to less thanor equal to about 5.5 wt. %; iron at less than or equal to about 0.15wt. %; chromium at greater than or equal to about 0.25 to less than orequal to about 0.35 wt. %; magnesium at greater than or equal to about0.1 to less than or equal to about 0.5 wt. %; zinc at less than or equalto about 0.01 wt. %; titanium at greater than or equal to about 0.05 toless than or equal to about 0.1 wt. %; phosphorus at less than or equalto about 0.003 wt. %; strontium at greater than or equal to about 0.01to less than or equal to about 0.015 wt. %; and a balance of aluminum.In still other embodiments, the lightweight, high-strength caststructural component is formed of an aluminum-based alloy materialhaving a composition consisting essentially of silicon at greater thanor equal to about 4.5 to less than or equal to about 5.5 wt. %; iron atless than or equal to about 0.15 wt. %; chromium at greater than orequal to about 0.25 to less than or equal to about 0.35 wt. %; magnesiumat greater than or equal to about 0.1 to less than or equal to about 0.3wt. %; zinc at less than or equal to about 0.01 wt. %; titanium atgreater than or equal to about 0.05 to less than or equal to about 0.1wt. %; phosphorus at less than or equal to about 0.001 wt. %; strontiumat less than or equal to about 0.005 wt. %; and a balance of aluminum.In still other embodiments, the lightweight, high-strength caststructural component is formed of an aluminum-based alloy materialhaving a composition consisting of silicon at greater than or equal toabout 4.5 to less than or equal to about 5.5 wt. %; iron at less than orequal to about 0.15 wt. %; chromium at greater than or equal to about0.25 to less than or equal to about 0.35 wt. %; magnesium at greaterthan or equal to about 0.1 to less than or equal to about 0.3 wt. %;zinc at less than or equal to about 0.01 wt. %; titanium at greater thanor equal to about 0.05 to less than or equal to about 0.1 wt. %;phosphorus at less than or equal to about 0.001 wt. %; strontium at lessthan or equal to about 0.005 wt. %; and a balance of aluminum.

In certain aspects, the lightweight, high-strength cast structuralcomponent formed of such an aluminum alloy exhibits a yield strength ofgreater than or equal to about 270 to less than or equal to about 300MPa. The lightweight, high-strength cast structural component mayexhibit an elongation of greater than or equal to about 7% and morepreferably greater than or equal to about 9%.

As mentioned above, the cast structural component is lightweight. Morespecifically, the aluminum-based alloy material having compositionsaccording to the present disclosure is on average about 5 to about 10%lighter than a similar structural component cast of a conventionalaluminum alloy, such as A356. One exemplary, non-limiting composition ofA356 includes copper at less than or equal to about 0.05 wt. %; siliconat from greater than or equal to about 6.5 to less than or equal toabout 7.5 wt. %; magnesium at from greater than or equal to about 0.3 toless than or equal to about 0.45 wt. %; manganese at less than or equalto about 0.05 wt. %; titanium at from greater than or equal to about0.04 to less than or equal to about 0.15 wt. %; zinc at less than orequal to about 0.05 wt. %; iron at less than or equal to about 0.09 wt.%; manganese at less than or equal to about 0.05 wt. %; beryllium atless than or equal to about 0.0008 wt. %; trace elements at less than orequal to about 0.15 wt. %; and a balance of aluminum. As will beappreciated by those of skill in the art, such a composition of A356 isrepresentative, but the composition of A356 may vary somewhat from therepresentative values disclosed here depending on variation in thestandard used and other manufacturing parameters. Moreover, as notedabove, many metal parts can be made using the compositions according tothe present disclosure to form vehicle components. Vehicles having metalparts made using the compositions according to the present disclosuretherefore potentially translate to weight savings. Reducing the weightof components in part is important for improving efficiency and is ofgreat importance for fuel efficiency in mobile applications, such as inautomobiles.

As mentioned above, the cast structural component is high strength. Morespecifically, the aluminum-based alloy materials having compositionsaccording to the present disclosure exhibit a yield strength of greaterthan or equal to about 270 to less than or equal to about 300 MPa. Aconventional aluminum alloy, A356, on the other hand, exhibits a yieldstrength of only about 150-180 MPa. While not limiting the presentdisclosure to any particular theory, the addition of chromium to thealuminum alloy is believed to provide higher strength by providingnano-scale precipitation after T6 heat treatment.

The other elements incorporated in the aluminum-based alloy also offercertain benefits to the component as a whole. More specifically, by wayof limiting example, limiting the amount of iron is believed to preventthe formation of intermetallic phases, which would otherwisedramatically reduce ductility. Further, the presence of silicon isbelieved to provide good castability for thick wall castings. Thepresence of magnesium is believed to provide resistance to anti-coldcracking. The presence of titanium is believed to further improve theductility of the casting and reduce the risk of hot cracking. Finally,the presence of strontium is believed to provide eutectic phasemorphology control.

The low-pressure die casting processes preferable for use with thecompositions according to the present disclosure shall now be furtherdescribed. As described above generally, low-pressure die casting is aprocess where a metal melt is in a sealed furnace having a riser tube. Apressurized gas is added to the sealed furnace, which forces the metalmelt through the riser tube and into a die. According to the presentdisclosure, the casting temperature is controlled at a temperature ofgreater than or equal to about 715° C. to less than or equal to about730° C. to ensure the aluminum-based alloy is kept in a liquidus state.Controlling the temperature close to a temperature sufficient toliquidize the aluminum-based alloy is desired to reduce the amount ofdegassing necessary. Prior to casting, the aluminum-based alloy meltundergoes a degassing process sufficient to limit hydrogen in an amountof from greater than or equal to about 0.1 to less than or equal toabout 0.15 cc per 100 g of the aluminum-based alloy melt. The degassingmay be accomplished by ways known in the art, such as by introducingpurging gas bubbles. At least a portion of the aluminum-based alloy meltis introduced into the die and allowed to solidify. Once the castingsolidifies, the pressurized gas is released, the remainingaluminum-based alloy melt in the riser tube returns to the sealedfurnace, and the die opens to release the casting. The process may becompleted once the die is again closed.

The gravity casting process preferable for use in certain aspects withthe compositions according to the present disclosure shall now befurther described. As described above generally, gravity casting is aprocess where a metal melt is introduced into a die by a pouring cup ora ladle or the like. According to the present disclosure, the castingtemperature is again controlled at a temperature of from greater than orequal to about 715° C. to less than or equal to about 730° C. to ensurethe aluminum-based alloy is kept in a liquidus state. Controlling thetemperature close to a temperature sufficient to liquidize thealuminum-based alloy is desired to reduce the amount of degassingnecessary. Prior to casting, the aluminum-based alloy melt undergoes adegassing process sufficient to limit hydrogen in an amount of about0.15 cc per 100 g of the aluminum-based alloy melt. The degassing may beaccomplished by ways known in the art, such as by using a rotaryimpeller degasser in the ladle. Once the casting solidifies, the die isopened and the casting is removed.

The T6 heat treatment process preferable for use with the compositionsaccording to the present disclosure shall now be further described.First, a solution heat treatment is provided by heating the casting tofrom greater than or equal to about 535° C. to less than or equal toabout 545° C. for a period of greater than or equal to about eighthours. After providing the solution heat treatment, hot water quenchingat from greater than or equal to about 70° C. to less than or equal toabout 90° C. is then provided to the casting to rapidly cool the castingto prevent precipitation. Once the casting is cooled, an artificialaging treatment is provided at from greater than or equal to about 150°C. to less than or equal to about 175° C. from greater than or equal toabout 4 to less than or equal to about 20 hours.

Referring to FIG. 2, a flowchart showing the steps of preparing alightweight, high-strength cast structural component according to alow-pressure die cast method 200 is shown. A preferable aluminum-basedalloy comprises silicon at greater than or equal to about 4 to less thanor equal to about 7 wt. %; iron at less than or equal to about 0.15 wt.%; manganese at less than or equal to about 0.5 wt. %; chromium atgreater than or equal to about 0.15 to less than or equal to about 0.5wt. %; magnesium at less than or equal to about 0.8 wt. %; zinc at lessthan or equal to about 0.01 wt. %; titanium at greater than or equal toabout 0.05 to less than or equal to about 0.15 wt. %; phosphorus at lessthan or equal to about 0.003 wt. %; strontium at less than or equal toabout 0.015 wt. %; and a balance of aluminum.

The aluminum-based alloy is melted (e.g., heated to above its meltingpoint) to provide an aluminum-based alloy melt at 210. Thealuminum-based alloy melt undergoes low-pressure die casting at 220 tocreate a lightweight, high-strength cast structural component. Morespecifically, the aluminum-based alloy melt is introduced into a sealedfurnace kept at a temperature of from greater than or equal to about715° C. to less than or equal to about 730° C. Optionally, thealuminum-based alloy melt is degassed to limit hydrogen in an amount offrom about 0.1 to about 0.15 cc per 100 g of the aluminum-based alloymelt. The sealed furnace is connected to a riser tube, and the risertube is connected to a die. A pressurized gas is introduced into thesealed furnace, which forces the aluminum-based alloy melt through theriser tube and into the die. At least a portion of the aluminum-basedalloy melt is introduced into and fills the die and allowed to solidify.Once the casting solidifies, the pressurized gas is released, theremaining aluminum-based alloy melt in the riser tube returns to thesealed furnace, and the die opens to release the casting.

The casting is further subjected to T6 heat treatment at 230 to providea lightweight, high-strength cast structural component according to thepresent disclosure. More specifically, the casting is subject to asolution heat treatment wherein the casting is heated to from greaterthan or equal to about 535° C. to less than or equal to about 545° C.for a period of less than or equal to about eight hours. After providingthe solution heat treatment, hot water quenching at from greater than orequal to about 70° C. to less than or equal to about 90° C. is thenprovided to the casting to rapidly cool the casting. After cooling, thecasting undergoes an artificial aging treatment at from greater than orequal to about 150° C. to less than or equal to about 175° C. forgreater than or equal to about 4 to less than or equal to about 20 hoursto provide the a lightweight, high-strength cast structural componentaccording to the present disclosure. The lightweight, high-strength caststructural component according to the present disclosure exhibits ayield strength of greater than or equal to about 270 to less than orequal to about MPa, is greater than or equal to about 5 to less than orequal to about 10% lighter than a structural component cast ofconventional comparative A356 aluminum alloy, and may have an elongationof greater than or equal to about 7% or even greater than or equal toabout 9%.

Referring to FIG. 3, a flowchart showing the steps of preparing a caststructural component according to a gravity casting method 300 is shown.A preferable aluminum-based alloy comprises silicon at greater than orequal to about 4 to less than or equal to about 7 wt. %; iron at lessthan or equal to about 0.15 wt. %; manganese at less than or equal toabout 0.5 wt. %; chromium at greater than or equal to about 0.15 to lessthan or equal to about 0.5 wt. %; magnesium at less than or equal toabout 0.8 wt. %; zinc at less than or equal to about 0.01 wt. %;titanium at greater than or equal to about 0.05 to less than or equal toabout 0.15 wt. %; phosphorus at less than or equal to about 0.003 wt. %;strontium at less than or equal to about 0.015 wt. %; and a balance ofaluminum.

The aluminum-based alloy melt is melted (e.g., heated to above itsmelting point) to provide an aluminum-based alloy melt at 310. Thealuminum-based alloy melt undergoes gravity casting at 320 to provide acasting. More specifically, the aluminum-based alloy melt is introducedinto a die by a pouring cup or a ladle or the like at the liquidustemperature of from greater than or equal to about 715° C. to less thanor equal to about 730° C. Optionally, the aluminum-based alloy melt isdegassed to limit hydrogen in an amount of about 0.15 cc per 100 g ofthe aluminum-based alloy melt. Once the casting solidifies, the die isopened and the casting is removed.

The casting is further subject to T6 heat treatment at 330 to provide alightweight, high-strength cast structural component according to thepresent disclosure. More specifically, the casting is subject to asolution heat treatment wherein the casting is heated to from greaterthan or equal to about 535° C. to less than or equal to about 545° C.for a period of less than or equal to about eight hours. After providingthe solution heat treatment, hot water quenching at from greater than orequal to about 70° C. to less than or equal to about 90° C. is thenprovided to the casting to rapidly cool the casting. After cooling, thecasting undergoes an artificial aging treatment at from greater than orequal to about 150° C. to less than or equal to about 175° C. forgreater than or equal to about 4 to less than or equal to about 20 hoursto provide the a lightweight, high-strength cast structural componentaccording to the present disclosure. The lightweight, high-strength caststructural component according to the present disclosure exhibits ayield strength of greater than or equal to about 270 to less than orequal to about 300 MPa, is greater than or equal to about 5 to less thanor equal to about 10% lighter than a structural component cast of aconventional A356 alloy, and may have an elongation of greater than orequal to about 7%.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways.

Such variations are not to be regarded as a departure from thedisclosure, and all such modifications are intended to be includedwithin the scope of the disclosure.

What is claimed is:
 1. A method of forming a lightweight, high-strengthcast structural component comprising: casting an aluminum-based alloycomprising silicon at greater than or equal to about 4 to less than orequal to about 7 wt. %; iron at less than or equal to about 0.15 wt. %;manganese at less than or equal to about 0.5 wt. %; chromium at greaterthan or equal to about 0.15 to less than or equal to about 0.5 wt. %;magnesium at less than or equal to about 0.8 wt. %; zinc at less than orequal to about 0.01 wt. %; titanium at greater than or equal to about0.05 to less than or equal to about 0.15 wt. %; phosphorus at less thanor equal to about 0.003 wt. %; strontium at less than or equal to about0.015 wt. %; and a balance of aluminum to form the lightweight,high-strength cast structural component.
 2. The method of claim 1,wherein the lightweight, high-strength cast structural component has ayield strength of greater than or equal to about 270 MPa.
 3. The methodof claim 1, wherein the lightweight, high-strength cast structuralcomponent has an elongation of greater than or equal to about 7%.
 4. Themethod of claim 1, wherein the lightweight, high-strength caststructural component has an elongation of greater than or equal to about9%.
 5. The method of claim 1, wherein the casting is a low-pressure diecasting process.
 6. The method of claim 1, wherein the casting is agravity casting process.
 7. The method of claim 5, further comprising T6heat treating the lightweight, high-strength cast structural componentafter the casting.
 8. The method of claim 5, wherein the magnesium ispresent in an amount of greater than or equal to about 0.1 to less thanor equal to about 0.6 wt. % and the strontium is present in an amount ofgreater than or equal to about 0.01 to less than or equal to about 0.015wt. %.
 9. The method of claim 6, wherein the magnesium is present in anamount of greater than or equal to about 0.1 to less than or equal toabout 0.5 wt. %; the phosphorus is present at less than or equal toabout 0.001 wt. %; and the strontium is present in an amount of lessthan or equal to about 0.005 wt. %.
 10. A method of forming alightweight, high-strength cast structural component comprising: gravitycasting an aluminum-based alloy comprising silicon at greater than orequal to about 4 to less than or equal to about 7 wt. %; iron at lessthan or equal to about 0.15 wt. %; manganese at less than or equal toabout 0.5 wt. %; chromium at greater than or equal to about 0.15 to lessthan or equal to about 0.5 wt. %; magnesium at less than or equal toabout 0.8 wt. %; zinc at less than or equal to about 0.01 wt. %;titanium at greater than or equal to about 0.05 to less than or equal toabout 0.15 wt. %; phosphorus at less than or equal to about 0.003 wt. %;strontium at less than or equal to about 0.015 wt. %; and a balance ofaluminum.
 11. The method of claim 10, wherein the lightweight,high-strength cast structural component has a yield strength of greaterthan or equal to about 270 MPa.
 12. The method of claim 10, wherein thelightweight, high-strength cast structural component has an elongationof greater than or equal to about 7%.
 13. The method of claim 10,further comprising T6 heat treating the lightweight, high-strength caststructural component after the casting.
 14. The method of claim 10,wherein the magnesium is present in an amount of greater than or equalto about 0.1 to less than or equal to about 0.5 wt. %; the strontium ispresent in an amount of less than or equal to about 0.005 wt. %; and thephosphorus is present in an amount of less than or equal to about 0.001wt. %.
 15. A method of forming a lightweight, high-strength caststructural component comprising: low-pressure die casting analuminum-based alloy comprising silicon at greater than or equal toabout 4 to less than or equal to about 7 wt. %; iron at less than orequal to about 0.15 wt. %; manganese at less than or equal to about 0.5wt. %; chromium at greater than or equal to about 0.15 to less than orequal to about 0.35 wt. %; magnesium at less than or equal to about 0.8wt. %; zinc at less than or equal to about 0.01 wt. %; titanium atgreater than or equal to about 0.05 to less than or equal to about 0.15wt. %; phosphorus at less than or equal to about 0.003 wt. %; strontiumat less than or equal to about 0.015 wt. %; and a balance of aluminum toform the lightweight, high-strength cast structural component.
 16. Themethod of claim 15, wherein the lightweight, high-strength caststructural component has a yield strength of greater than or equal toabout 270 MPa.
 17. The method of claim 15, wherein the lightweight,high-strength cast structural component has an elongation of greaterthan or equal to about 7%.
 18. The method of claim 15, wherein thelightweight, high-strength cast structural component has an elongationof greater than or equal to about 9%.
 19. The method of claim 15,further comprising T6 heat treating the lightweight, high-strength caststructural component after the casting.
 20. The method of claim 15,wherein the magnesium is present in an amount of greater than or equalto about 0.1 to less than or equal to about 0.6 wt. and the strontium ispresent in an amount of greater than or equal to about
 0. 01 to lessthan or equal to about 0.015 wt. %.